1. Field of the Invention
The present invention relates in general to the field of dilatation or balloon catheters employed in the treatment of vascular diseases. More particularly, the present invention relates to a dual-lumen low-profile balloon catheter assembly with perfusion ports communicating proximally and distally of the dilatation balloon via a lumen of the catheter. An axially movable inner guide sheath receives a guide wire assembly for the catheter. Distal ends of the guide sheath and guide wire are movable across the perfusion ports in the proximal direction to allow blood perfusion flow through the full cross sectional area of the catheter lumen. When the guide sheath is moved across the perfusion ports in the distal direction it allows the distal end of the guide wire to traverse these ports with no possibility that the wire end will escape through these ports, improving patient safety.
2. Related Technology
Over the past decade the medical procedure known as angioplasty has become widely accepted as a safe and effective method for treating various types of vascular diseases. For example, angioplasty is widely used for opening stenoses throughout the vascular system and particularly for opening stenoses in coronary arteries.
At present, the most common form of angioplasty is called percutaneous transluminal coronary angioplasty (PTCA). This procedure utilizes a dilatation catheter having an inflatable balloon at its distal end. By using a fluoroscope and radiopaque dyes and markers on the catheter for visualization the distal end of the dilatation catheter is guided into position through a guide catheter and across the stenosis. With the dilatation balloon is in this position of alignment with the stenosis the balloon is inflated for a brief duration to open the artery and establish adequate blood flow.
Typically, inflation of the balloon is accomplished by supplying pressurized fluid from an inflation apparatus located outside the patient's body through an inflation lumen in the catheter which communicates with the balloon. Conversely, applying a negative pressure to the inflation lumen collapses the balloon to its minimum dimension for initial placement or for removal of the balloon catheter from within the blood vessel receiving treatment.
In the past years a number of balloon catheter designs have been developed which have contributed to the safety and acceptability of PTCA and similar medical procedures. The most common design is known as an "over-the-wire" balloon catheter. This conventional device typically utilizes a relatively large lumen for passage of a guide wire and injection of contrast fluid (or angiographic visualization dye) to assist in the placement of the device. A second parallel lumen is provided for inflation and deflation of the balloon.
Typically, a steerable guide wire is positioned within the larger lumen and the entire assembly is maneuvered into an initial position within the target artery through a guide catheter which has been positioned previously, and which is of sufficient diameter to pass the angioplasty catheter. Once near the site of the stenoses the guide wire can be rotated and axially extended or retracted into position across the lesion. The therapeutic angioplasty catheter is subsequently advanced along the guide wire to position its balloon end portion across the lesion prior to inflation of the balloon and dilatation of the stenosis.
An alternative conventional over-the-wire catheter assembly utilizes a non-removable guide wire that allows for longitudinal or axial movement. However, this design has a significant drawback because the entire catheter assembly with its non-removable guide wire must be removed to accomplish replacement or exchange of the balloon. In some cases of PTCA it is necessary to replace the balloon with one of different diameter or configuration following the initial dilatation.
However, cases of acute reclosure have been noted where the lesion closes again following dilatation and removal of the balloon catheter. One response to this reclosure problem has been the placement of an expandable stent into the artery at the lesion with another replacement balloon catheter. This alternative system increases the difficulties of these subsequent procedures by requiring that the replacement catheter renegotiate the entire placement path without the advantage of a guide wire.
A "monorail" variant of the standard balloon-over-a-wire system also has been developed in which only the distal portion of the balloon catheter tracks over the guide wire. This system utilizes a conventional inflation lumen and a relatively short guiding or through lumen adjacent to the distal end of the catheter. Principal benefits of the monorail construction of therapeutic catheter are the reduction of frictional drag over the length of the externally located guide wire and the ease of balloon exchange. This construction provides the ability to recross an acutely closed vessel or to exchange balloons without removing the guide wire.
However, a disadvantage of this "mono-rail" design is the increased difficulty in steering the guide wire because the guide wire is not supported by the balloon catheter. Also, the balloon catheter itself may not be pushable to move along the guide wire. Some versions of the monorail use an external flexible pusher member which also tracks the guide wire and is used to move the therapeutic catheter to the desired location near the distal end of the guide wire. Additionally, the dual lumen distal design of the monorail catheters produces a larger profile and catheter shaft size.
Another innovation in dilatation catheter design which is now conventional is the "fixed-wire" or integrated "balloon-on-a-wire" dilatation catheter. These single lumen designs utilize a relatively narrow wire positioned within the inflation lumen and permanently fixed to the distal end of the balloon. This construction produces a low-profile catheter assembly which is able to cross severely narrowed lesions and to navigate tortuous vascular pathways. Additionally, the fixed guide wire bonded at the distal end of the balloon improves the steerability and pushability of these designs which enhances their maneuverability. The thin shaft design also improves coronary visualization and enables all but the tightest critical lesions to be crossed.
However, though able to provide relatively quick and simple balloon placement as well as providing access to lesions otherwise unsuitable for PTCA, fixed-wire balloon-on-a-wire systems sacrifice the ability to maintain guide wire position across the lesion when exchanging balloons or the safety advantage of being able to recross an acutely closed vessel without repositioning the entire assembly.
Yet another difficulty arises when the dilatation balloon is inflated to dilate the vessel under treatment. While this balloon is inflated blood cannot circulate in the vessel. This lack of blood circulation can lead to necrosis of tissues already stressed by the previously reduced level of blood flow. As a solution to this problem, catheters have been provided with perfusion ports proximal and distal to the balloon and communicating with one another via a lumen of the catheter which extends through the balloon.
A conventional catheter of this type is known from U.S. Pat. No. 4,581,017, issued 8 Apr. 1986 to H. Sahota. This catheter includes a dual or multi lumen flexible shaft with a dilatation balloon carried on the shaft. Perfusion ports proximally and distally of the dilatation balloon allow perfusion blood flow.
A conventional catheter of this latter type is also depicted in U.S. Pat. No. 5,160,321, issued 3 Nov. 1992, to H. Sahota. The catheter depicted in the Sahota patent employs a separate inner lumen to outwardly bound an annular axially extending passage through which blood may flow past the inflated balloon via perfusion ports. Also, this separate inner lumen inwardly defines a passage through which the guide wire assembly for the catheter extends.
However, with catheters of the type illustrated by the Sahota patent, and others of this type, the distal portion of the catheter is obstructed by the guide wire, or by the guide wire and its lumen. Consequently, the cross sectional area of the catheter lumen which is available for blood perfusion past the inflated balloon is very limited. While the distal end portion of the catheter may be made of a size sufficient to pass an adequate volume of blood, this size increase is contrary to the recognized advantages of having a low-profile catheter.
Alternatively, it has been proposed to withdraw the guide wire proximally of the perfusion ports prior to inflation of the dilatation balloon in order to make a larger part of the perfusion lumen available for blood flow. However, a serious disadvantage arises when the guide wire is again advanced in that the distal tip of the guide wire may inadvertently pass outwardly of the catheter through one of the perfusion ports. The Sahota patent recognizes the risk of this possibility, and provides the inner guide wire lumen as a partial and not completely satisfactory solution to this problem.